This Der Spiegel article was posted earlier by someone else, but resulted in zero discussion:
Doomed Flight AF 447: Questions Raised about Airbus Automated Control System - SPIEGEL ONLINE - News - International
Several of the points raised in this article have not even been touched upon by this group - in particular the potentially detrimental role of the horizontal stabilizer and the questioned culpability (beyond human error) of EASA, Thales (pitot tubes) and potentially Airbus...
But why would co-pilot Bonin pull up instead of pushing the nose down? It wasn't long before the plane's angle became dangerously high.
An explanation for the A330's rising nose, however, could also be provided by a line in the BEA report referring to the trimmable horizontal stabilizer. Situated at the tail of the aircraft next to the flaps controlling the aircraft's pitch, known as the elevator, the horizontal stabilizer likewise helps control the plane's horizontal stability.
According to the BEA's interim report, the horizontal stabilizer moved from three degrees to 13 degrees, almost the maximum. In doing so, it forced the plane into an increasingly steep climb. It "remained in the latter position until the end of the flight," the report notes.
Gerhard Hüttig, a professor at the Institute of Aeronautics and Astronatics at the Technical University in Berlin, considers the high angle of the horizontal stabilizer to be a failure of the Airbus' electronic flight control system. Hüttig, a former Airbus pilot himself, calls it "a programming error with fatal consequences."
"No matter how hard the crew tried to push down the nose of the aircraft, they would have had no chance," Hüttig says.
Exactly what orders [Captain Marc Dubois] issued [after re-entering the cockpit] are not part of last Friday's report. But sources close to the investigation are saying that he said: "This is a stall. Reduce power and nose down!"
This order would have been the correct one were the situation not already hopeless. By that time, the jet, which was pointing steeply upwards, was already losing vertical altitude at a rate of 200 kilometers per hour.
Indeed, the BEA report documents efforts undertaken following the captain's return to bring the plane's nose down. Forty-one seconds before impact, both co-pilots were pushing on the controls. Then Bonin cried desperately: "Go ahead, you have the controls." There were just 30 seconds left before the end.
But why were all the crew's efforts in the cockpit in vain? Did the plane no longer react to the cockpit commands as it fell? Or did the horizontal stabilizer, which was still almost fully deflected at 13 degrees, continue to force the nose of the plane up?
Hüttig, who also advises the victims' families regarding technical issues, is concerned about the description of the horizontal stabilizer as being at 13 degrees. That is consistent with behavior he observed in an Air France A330 simulator in Paris a few months ago, when he replicated the situation together with other pilots. "The phenomenon is startlingly similar," he says.
Was it really the stabilizer that doomed the pilots? In theory, they could still have adjusted it -- its position can be manually altered using a wheel near the thrust levers. But as Hüttig notes, one would first have to know that the stabilizer is deflected.
Huttig pointed out that Airbus published a detailed explanation of the correct behavior in the event of a stall in the January issue of its internal safety magazine. "And there, all of a sudden, they mention manually trimming the stabilizers," he says.
It remains an open question who will be proved right at the end of the investigations. But it is already clear that no one individual will bear the burden of responsibility alone. The pilots could have stabilized the aircraft if they had reacted differently. But the airline had also probably not prepared them properly for such a situation. Similarly, Airbus' recommendations were insufficient. That much is spelled out in the files of the French authorities which investigated the crash of the A330. "To date," the experts say, the deficiencies have "not been rectified."
The Pitot Tubes and culpability of EASA?
As stated in the report (2h 10min 05sec) the autopilot and auto-thrust disengaged due to icing of the pitot tubes (manufactured by Thales - see below) which resulted in loss of speed readings.
If the speed sensors fail, it has a "particularly confusing" effect in Airbus models, the experts say, pointing to the high degree of automation in the cockpit. "If the control computers, which are actually supposed to provide more safety, fail, then the automatic systems can become a danger at that moment," says William Voss, president of the Flight Safety Foundation.
The manufacturer Thales was well aware of the catastrophic consequences of a failure of the speed sensors as early as 2005. At the time, the French company concluded that such a failure could "cause plane crashes."
A total of 32 cases are known in which A330 crews got into difficulties because the speed sensors failed. In all the cases, the planes had pitot sensors from Thales, which were significantly more prone to failure than a rival model from an American manufacturer.
But none of the responsible parties intervened. In 2007, Airbus merely "recommended" that the sensors be replaced. Air France took that as a reason not to carry out the costly work -- and it even got official blessing for doing so. The European Aviation Safety Agency wrote that it currently saw "no unsafe condition that warrants a mandatory modification of the Thales pitot tubes."
Several comments have been made here claiming that the passengers wouldn't have noticed anything...(I wish it were true)
The passengers, who had just a short time before been pressed into the backs of their seats, were now being held into their seats only by their seatbelts. "At this moment, I would have feared for my life even if I was sitting in the passenger cabin," said one A330 pilot after reading the BEA report. That the plane was in freefall would have been clear to all on board. The nose of the plane pointed skyward at an angle of 16 degrees. "That's more than immediately following takeoff," the pilot said.